Ya tengo escrita la reseña, pero todavía me falta revisar la bibliografía.

Both are possible, but they are not exactly the same.

• He escrito la reseña = I have written the review. This is the standard perfect tense and focuses on the completed action.
• Tengo escrita la reseña = literally something like I have the review written. This focuses more on the result or state: the review is done and is now in a written, finished condition.

In this sentence, tengo escrita sounds very natural because the speaker is contrasting what is already finished with what still remains to be done.

Because escrita agrees with la reseña, which is feminine singular.

Here, the participle is not forming a tense like he escrito. Instead, it behaves more like an adjective describing the noun:

• la reseña escrita = the written review

So it must match the noun:

• el informe escrito
• la reseña escrita
• los artículos escritos
• las cartas escritas

That is why tengo escrita la reseña uses escrita.

Ya means already. It tells you that this part of the task is completed at this point.

So:

• Ya tengo escrita la reseña = I already have the review written

It also helps create a contrast with todavía later in the sentence:

• ya = already done
• todavía = still not done

That contrast is one of the main ideas of the whole sentence.

This is a very common Spanish pattern. Faltar often works from the perspective of what is still missing or remaining.

So:

• Me falta revisar la bibliografía literally means something like Reviewing the bibliography is still lacking to me
• Natural English: I still need to review the bibliography or I still have to review the bibliography

The important thing is that Spanish often expresses this idea with faltar, while English usually says need to, have to, or still have left to do.

Because me is an indirect object pronoun, and with a conjugated verb it normally goes before the verb:

• me falta
• te falta
• le falta
• nos falta

Here, me means to me / for me in a grammatical sense, even though the best English translation is simply I still need to...

So:

• me falta revisar la bibliografía = I still need to review the bibliography

Because after faltar, Spanish can use an infinitive to say what action remains to be done.

So:

• Me falta revisar la bibliografía = I still need to review the bibliography
• Me falta terminar el informe = I still need to finish the report
• Me falta llamar a Marta = I still need to call Marta

The infinitive names the action that is still pending.

Yes.

1. Todavía and aún

In this sentence, todavía and aún mean the same thing:

• pero todavía me falta revisar la bibliografía
• pero aún me falta revisar la bibliografía

In everyday speech, todavía is often more common and neutral.

2. Position

The position used here is very natural:

• pero todavía me falta revisar la bibliografía

You may also hear:

• pero me falta todavía revisar la bibliografía

That is possible, but the original version sounds more neutral and straightforward.

Yes, absolutely. That would be a very natural sentence too.

The difference is mainly one of nuance:

• Ya tengo escrita la reseña emphasizes the result: the review is already done.
• Ya he escrito la reseña emphasizes the completed action: I have written it.
• Me falta revisar... emphasizes what remains.
• Tengo que revisar... simply states an obligation or pending task.

So the original sentence feels slightly more focused on task progress and completion status.

Because the speaker is referring to specific things, not to reviews or bibliographies in general.

• la reseña = the specific review we are talking about
• la bibliografía = the specific bibliography connected with that work

English sometimes uses articles differently, so this can feel strange to learners. In Spanish, if both speaker and listener know which review and which bibliography are meant, using la is normal.

Yes. Ya tengo escrita la reseña and Ya tengo la reseña escrita are both correct.

Both mean essentially the same thing, but the rhythm and emphasis can shift slightly:

• tengo escrita la reseña puts the participle closer to the verb
• tengo la reseña escrita places the object first and can feel a bit more concrete: I have the review written

Native speakers use both patterns. The version in your sentence is completely natural.